Isolation of 4-aminopyridine resistant mutants affecting alkali-insoluble glucan content of cell walls in Saccharomyces cerevisiae.

Saccharomyces cerevisiae cells when grown on synthetic medium plates containing 10 mM of 4-aminopyridine (4-AP) undergo cell lysis. Using an ethylmethane sulfonate mutagenesis (EMS) screen, 4-AP resistant mutants (apr) were isolated which could grow on inhibitory concentration of 4-AP. Eighty mutants were obtained that were recessive, monogenic and formed two complementation groups. To identify genes, whose products might be interacting with the apr loci, extragenic suppressors were isolated, which reverted 4-AP resistance phenotype of apr mutants. The suppressors, when genetically characterized, were found to be recessive and represented two loci with overlapping functions. Representative alleles from apr mutants were analyzed for cell wall composition. They were found to have a higher amount of alkali-insoluble glucan signifying the role of alkali-insoluble glucan in cell wall maintenance.

Oscilaçöes do potássio sérico em pacientes submetidos a laparotomias / Seric potassium behavior in laparotomy submitted patients

Inúmeras pesquisas têm sido conduzidas, visando estudar o metabolismo do potássio sob os mais diferentes aspectos. O objetivo deste trabalho foi verificar o comportamento do íon potássio em pacientes submetidos a laparotomias. Foram estudados 53 pacientes operados com anestesia geral (cirurgias de médio e grande portes), avaliando-se a variação individual deste íon no pré e pós-operatório imediato e comparando-se com o grupo-controle de 20 pacientes submetidos à herniorrafia inguinal e 20 doentes internados por infarto agudo do miocárdio no Hospital Municipal de Santo André-São Paulo, ligado à FMABC. Observou-se no grupo das laparotomias, queda do potássio em 47,2 por cento, resultado estatisticamente significante, quando comparado com o grupo dos IAM (30 por cento) e das herniorrafias (10 por cento). Esta queda, porém, apenas ultrapassou os valores mínimos da normalidade em 32 por cento dos casos, sendo esta diferença não significante, concluindo-se que a reposição deste íon deva estar relacionada à sua dosagem no POI

Na+i, K+i and Cl-i regulation of exocytosis in guinea-pig antral mucous cells

Effects of intracellular Na+, K+ and Cl- on Ca(2+)-regulated exocytosis activated by 10 microM acetylcholine (ACh) were studied in guinea-pig antral mucous cells which are permeabilized by nystatin treatment. Ca(2+)-regulated exocytotic events were modulated by [Na+]i, [K+]i and [Cl-]i via mediation of PTX-sensitive G proteins. Increases in [Na+]i and PTX inhibit G protein (G(Na)), which suppressed the exocytosis. Increases in [K+]i caused the exchange of G proteins (from G(Na) to G(K)) to increase, and GK evoked activation of the exocytosis and was inhibited by PTX. Increases in [Cl-]i and PTX inhibit G protein (G(Cl)), which stimulates exocytotic events. Based on these observations, the exocytosis in antral mucous cells were modulated by intracellular ions, concentration of which were increased or decreased by cell volume changes caused by Ach.

Rol del endotelio en el efecto vasodilatador de la acetilcolina cuando el vaso aislado se somete a la acción contráctil de norepinefrina o de potasio / Role of endothelium in the vasodilator effect of the acetylcholine when the vaso isolated with endothelium contratedeith no repinephrine of potassium chloride

La acetilcolina depende de la conservación del endotelio vascular, para producir su efecto vasodilatador que es ocasionado por la liberación de un factor relajador derivado del endotelio y que corresponde al óxido nítrico. Se estudiaron las acciones de la acetilcolina, en manguitos aislados de aorta de rata con endotelio, contraídos por norepinefrina o cloruro de potasio. Se ensayaron dosis únicas de norepinefrina, 10-6 M y también dosis crecientes y acumulativas desde 10-8 hasta 10-4 antes y después de la incubación con acetilcolina. Además, se sometió la preparación con endotelio a los efectos de una solución despolarizante de potasio y luego se le agregó acetilcolina 10-3. También se observaron los efectos de la acetilcolina añadida previamente a la solución despolarizante. A modo de control, en otra serie experimental, se utilizó solución Krebs-Henseleir. La acetilcolina adicionada previamente a la solución de potasio antagoniza la contracción producida por esta solución despolarizante. En cambio, cuando la preparación es contraída previamente con dicha solución la acetilcolina no produce vasodilatación. La incubación en acetilcolina disminuye la acción contráctil de dosis creciente y acumulativas de norepinefrina, probablemente por liberación de factor de relajación derivado del endotelio

Evidence for neuronal release of isotopically labelled glycine from the rat ventral medullary surface in vivo

Spontaneous and stimulus-induced release of isotopically labelled glycine was studied in the superfused rat dorsal or ventral medullary surface in vivo. Superfusion of the ventral medullary surface of anesthetized (urethane, 1.2 g/kg, ip) male adult Wistar rats (250-350 g) with high K+ (40 mM) surrogate cerebrospinal fluid (CSF) produced an average increase of 45 per cent over the spontaneous efflux of exogenously applied glycine (N = 5, P<0.01). In experiments in which the calcium of the CSF was replaced by an equimolar amount of magnesium, the increase in glycine efflux in response to high K+ was reduced to 15 per cent, a value not statistically different from that observed in control experiments (N = 6). Veratridine stimulation evoked a large (80 per cent) increase in glycine efflux (N = 5, P<0.001), which was inhibited by tetrodotoxin. High potassium or veratridine failed to modify spontaneous release of glycine on the dorsal medullary surface. Results obtained in control experiments showed that neither high K+ nor veratridine is effective in modifying spontaneous efflux of [(3)H]-leucine or [(3)H]-inulin on the ventral or dorsal medullary surface. These data support the hypothesis that glycine is a neurotransmitter on the ventral medullary surface and that it may be part of neural pathways involved in cardiorespiratory regulation present in this region.

Mechanism of potassium transport across proximal tubule epithelium in the rat

The mechanism of proximal tubule potassium reabsorption was studied by stopped-flow microperfusion and determination of potassium activities by ion-sensitive resin microelectrodes. The proximal tubule was unable to establish transepithelial potassium gradients. perfusion with 20 mM K+ turned the lumen 3 mV more negative, an effect abolished by Ba2+. the half-time for K+ activities to reach their stationary level after perfusion with 1 mMK+ was significantly increased by Ba2+ from 4.25 ñ 0.14sto 11.0 ñ 1.71s, and aftr perfusion with 20 mMK+, from 5.43 ñ 0.20 to 12.53 ñ 0.90s. These data indicate that a significant fraction of potassium is transferred across proximal tubule spithelium by a transcellular, K+-channel-dependent route